1. Field of the Invention
This invention generally relates to a surface acoustic wave (hereinafter referred to as SAW) device that employs a piezoelectric material, and more particularly, to a SAW device having multiple interdigital transducers (hereinafter referred to as IDT) that are provided on a piezoelectric substrate, and to wireless devices that employ the same. This SAW device is of a longitudinal coupling multi-mode type.
2. Description of the Related Art
The SAW filters are widely used for high-frequency circuits on wireless devices as filters. The wireless devices are represented by mobile telephones or the like. In recent years, integrated circuits (ICs) that perform a balanced input and output operation have been employed for the high-frequency circuits of the wireless devices. Subsequently, the SAW filter is also required to perform the balanced input and output operation. Conventionally, as an example of realizing the balanced operation, Japanese Patent Application Publication No. 6-204781 (hereinafter referred to as Document 1) discloses a method of using electrodes as input and output terminals. One electrode that faces the IDT on the input side is used for an input terminal, and the other electrode that faces the IDT on the output side is used for an output terminal. Also, as another example, Japanese Patent Application Publication No. 11-97966 (hereinafter referred to as Document 2) discloses that the IDTs are divided into two groups, that is, input group and output group. The balanced operation is realized by operating those two groups that are 180° out of phase.
It is to be noted that there are problems in the conventional techniques disclosed in Documents 1 and 2. Specifically, a stray capacitance is generated between the IDT on the input side and that on the output side, and the symmetry is bad between balanced operation signals. Thus, electronic devices equipped with the SAW filters such as wireless devices may malfunction.